Thermal-stretching apparatus for yarn



u IN1/mmm R. F. CONAWAY Filed June 4, 1946 YARN THERMAL-STRETCHING APPARATUS FOR YARN Dec.. M, 1948.

Patented Dec. 14, 1948 THERMAL- STRETCHING APPARATUS FOR YARN Rollin F. Conaway, Waynesboro, Va., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation oi Delaware Application June 4. 1946, Serial No. 674,353

2 Claims. l

This invention relates to the manufacture of artificial filaments, yarn and thread and, more particularly, to improvements in apparatus for the thermal-stretching of filaments of thermoplastic artificial material such as cellulose acetate.

In United States Patent No. 1,921,426 (Niogret) there is disclosed a process for increasing the tensile strength of artiiicial yarns which comprises rendering the yarn plastic by heating it in the dry state and subjecting the heat-plastic yarn to stretching tensions. In practice, this process is most conveniently carried out by passing the yarns through a relatively long and narrow stretching cell wherein the yarn is subjected to dry heat produced by any suitable means inside or out of the cell. The draw-olf 4speed of the yarn from the cell is, of course, so adjusted as to impose the desired degree of stretch on the heat-softened yarn.

A serious defect of this otherwise simple and economical arrangement is that in the processing of cellulose acetate and other synthetic yarns which readily accumulate charges of static electricity, the accumulated charge may have one or several of the following eiects on the yarn within the cell:

(1) A swirling action within the cell may arise which causes the yarn at some points to approach very closely to the cell wall resulting in uneven heating with consequent variations in the tension required to stretch the yarn.

' (2) The yarn does not swirl, but intermittently contacts the cell walls for short lengths and then again is drawn into the axial line of the cell, resulting in uneven heating of the yarn and occasional breakage of individual filaments of th yarn. v

(3) The yarn may contact the cell wall for a period of time sum'cient to melt the thread, causing a break.

In all of these cases serious fluctuations in the physical properties oi the yarn are the result. The effects of static can, in some cases, be relieved by the application of large amounts of ordinary finish or by the use of a special anti-static iinish containinga substance .capable of conducting electricity. Such finish applications, however, cannot always be reconciled with ilnish applications desired for other textile purposes, in which event some other expedient for overcoming the eiiect of static charges must be found.

An object of this invention therefore is to provide means for overcoming the eiects of` static charges which accumulate in artificial thermoplastic yarns, such as cellulose acetate, under- 2 going dry heat-stretching, which means are operative irrespective of the finish composition. if any. present on the yarn.

A further object is to provide improvements in stretching cell construction whereby the harmful eiiects of static charges on the yarn treated therein are substantially eliminated and the path of the yarn through the cell is stabilized in a straight line.

A still further object is to provide yarn inlet means for a stretching cell which operates to overcome the harmful eil'ects of static charges in the yarn and hence to stabilize stretching tens ons.

These and other objects will moreY clearly appear from the following description.

In pursuance of tlese objectives, I have found that the path of the yarn being stretched may be stabilized to a straight line path through the cell by insertion of a small tube at the top (and preferably concentric with the walls) of the stretching cell, through which tube the yarn is passed into the cell.

Referring to theaccompanying ydrawing wherein:

Figure 1 is a cross-sectional view of a stretching cell provided with the novel yarn inlet means of this invention; and

Figure 2 is an enlarged scale, cross-sectional view detailing a modied form of yarn inlet means; the reference numeral I indicates-a relatively long, narrow and preferably cylindrical tube constrlcted at the ends to provide yarn guides to guide the yarn along the longitudinal axis of the tube which tube is surrounded in spaced relationship by a jacket or outer tube 2. In this form of stretching cell, the yarn passing through'tube I on a line coinciding with the longitudinal axis of the tube is heated mainly by radiant heat provided by a heating element 3 adjacent the inside wall of tube I and constructed, for example, of Nichrome ribbon. Additional heat is furnished by heating element 4 located adjacent the outer wall and extending substantially the full length of tube I. The foregoing4 is illustrative of a representative dry heat, thermal-stretching cell to which the improvement of the present invention is applicable. In accordance with the principles of this invention the inlet end of the stretching cell is provided with a small, substantially cylindrical yarninlet tube 5 extending into tube I and further disposed with its longitudinal axis in coincidence with the longitudinal axis of tube I. Insert tube 5 may be fabricated from any desirable material,

auch

' ably be small to permit rapid penetration oi heat.

The diameter of the insert tube should be appreciably smaller than that oi the heated stretching tube l, but must be suiiiciently large to permit easy Stringing o! the yarn through the tube. The length of the insert tube will depend on the total length of the stretching tube and the speed at which the yarn is passed therethrough and is readily determinable in each instance.. In general, a tube length of about to 20% the length of the stretching cell may be used effectively; The inside diameter of the starting tube should benot more than 50% the inside diameter of the stretching cell. With a foot stretching cell and a yarn input speed of 220 yds/min., insert tubes of 12 to 18 inches have operated satisfactorily. However, the insert tube must be short enough so that no appreciable amount of yarn stretch takes place therein.

In the modified form of insert tube shown in Fig. 2, constrictions 6 (which may be of any desirable coniiguration) are placed at various points in the tube 5', which constrictions together with the constricted lower end of the tube serve as yarn guides and to reduce to a minimum contact (and hence drag) of the yarn with the inner i wall surface of the insert tube.

The following example further illustrates the practice and attendant advantages of this invention:

Example A 'l0-denier, l-illament cellulose acetate yarn was stretched at an input speed of 220 yards per minute and a draw ratio of 1.75 through a heated tube 10 feet long and 1?/4 inch in diameter. The yarn being stretched wavered within the tube and tensions at the lower end varied through a wide range. An aluminum tube 15 inches long and if inch in diameter, with 0.022 inch wall thickness, was then inserted down the center of the heated stretching tube so that the upper ends of the two tubes were at the same level and the yarn being stretched was threaded through it. The path of the yarn being stretched then became a straight line down the center of the heated tube and the tensions at the lower end became uniform.

From the foregoing it will be manifest that the improvement constituting the present invention is easily applied to existing thermal stretch equipment, is inexpensive to make, is simple and trouble-free in operation, and permits the preparation of high-quality, heat-stretched articial yarn of uniform properties.

As many widely di'iierent embodiments of invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be restricted in any way except as defined in the appended claims.

I claim:

1. In apparatus for the dry heating and thermal stretching oi artificial thermoplastic filaments,'yarns, threads and like iilamentary structures which comprises a heated long cell having a yarn inlet opening at one end of said cell and a yarn outlet opening at the opposite end whereby yarn treated in said cell traverses the length thereof, the improvement which comprises a yarn inlet means consisting of a tube, small relative to the size of the cell and projecting into the inlet end of said cell a distance of from 5% t0 20% of the length of said cell and aligned on the longitudinal axis of said cell.

2. In a dry heating and thermal stretching apparatus comprising a long thin cylindrical cell, means for passing yarn under stretching tension through said cell in a path corresponding to the longitudinal axis of the cell and means for heating the cell, the improvement which consists of a. substantially cylindrical tube, small relative to the size of the cell, projecting a substantial distance into the cell on a line corresponding to the longitudinal axis of the cell andl adapted to receive and guide into said cell the yarn to be heated and stretched, the length of said tube being from 5% to 20% of the length of said cell, and the inside diameter of said tube being not more than of the inside diameter of said cell.

ROLLIN F. CONAWAY.

REFERENCES CITED rihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,498,738v Lahousse June 24, 1924 1,722,797 Jessup July 30, 1929 2,005,580 Ferre June 18, 1935 2,334,288 Reel Nov. 16, 1943 2,360,352 Lodge Oct. 17, 1944 2,371,579 Cole et al Mar. 13, 1945 2,398,856 Reel Apr. 23, 1946 2,402,228 Jackson et al. June 18, 1946 2,402,609 De Brabander June 25, 1946 

